Fibres – generally speaking – are among the most common and important samples that can be found in a forensic scenario. Their importance derives from the fact that they can be very easily transferred from one surface to another, allowing fibres to be linked to a suspect and later to a crime scene. In fact, it is possible to find many types of fibres at a crime scene.
Fibres can be grouped into two broad sets:
- Natural: these are animal (hair, wool, silk, etc.), vegetable (cotton, linen, hemp, jute, etc.) or mineral (asbestos);
- Artificial: they are subdivided into synthetic fibres if they are produced from synthetic polymers (nylon) and regenerated fibres if they are produced by chemically modifying a polymer already naturally present within the fibre.
In forensic analysis, the importance of these filaments depends on their characteristics: for example, man-made fibres are those with special, discriminating properties that lend themselves best to laboratory examinations.
Industrially, fibres are coloured with synthetic dyes. These, in order to be distinguished, are classified by a number called Colour Index (CI). This index is used to classify the chemical dyes based on their chemical structure, which consists mainly of nitrogen atoms, anthraquinones, carbonyls, etc.
By determining the structure of the chemical dye and therefore subsequently its CI, it is possible to link a test to a manufacture and thus help in the resolution of the investigation. Consequently, analyses of hair and hairs show which part of the body they come from, whether they are human or animal, the presence of particular brittlenesses, if they have undergone chemical or cosmetic treatment, and if they have fallen out spontaneously or if they have been taken off during a fight.
In Forensic Science, their importance is unquestionable because in cases of murder or assault they are often found on the victim’s body, held between the hands, under the fingernails or on the bed sheets. Forensic biological examination aims to identify biological stains at the crime scene or on evidence. During investigations, hair, both human and animal, is one of the biological samples that can be found and which can lead operators to identify the offenders. The hair bulb can be used in forensic genetics examinations to get a DNA match, because only within the bulb are traces of nucleated cells present that allow operators to extract DNA and perform a genetic profile. In fact, human hair found at crime scenes or on evidence can be used in forensics to obtain a DNA match between the hair and the suspect or victim, while animal hair can be used to obtain a DNA match between animal hair found at crime scenes and the offenders’ pets. Hair examination is mainly based on microscopy, which can allow the forensic hair analyst to identify a hair as being of animal origin, to characterise it for a particular species and to conduct comparative examinations, all while focusing on the morphological characteristics of the hair itself.
Therefore, it is necessary to employ comparative techniques, and thus observe the sample found at the scene with other available samples.
Fibres can be collected from clothes, carpets or car interiors, etc., and can be collected with disposable or sterile tweezers, although the most commonly used sampling technique involves using adhesive tape, pressing it directly onto the surface to be sampled.
About the Author
Ms. Chiara Lucanto is a Forensic Biologist and Academic Content Writer (email@example.com).